Konig



H. KONIG Oct. 10, 1961 SELECTIVE CALL-RECEIVING DEVICE IN COMMUNICATIONSYSTEMS Filed June 5, 1959 2 Sheets-Sheet 1 fmysmaf H. KONIG SELECTIVECALL-RECEIVING DEVICE IN COMMUNICATION SYSTEMS Filed June 5, 1959 2Sheets-Sheet 2 Hired States Patent ri"ice 3,004,241 SELECTIVECALL-RECEIVINGDEVICE IN COMMUNICATION SYSTEMS Heinrich Konig, Zurich,Switzerland, assignor to Albiswerk Zurich A.G., Zurich, Switzerland, acorporation of Switzerland Filed June 5, 1959, Ser. No. 818,290 Claimspriority, applicationSwitzerland June 6, 1958 l 6 Claims. (Cl. 340-164)f My invention relates to a method for selectively calling one ofy agroup of receivers by meansiof a signal-code of selector pulses whoserespective durations or mutual time spacings serve as selectioncriteria, and to a device for receiving such coded call signals. i

Known selective call methods in which the lengths of pulses or spacesdetermine theselcction of one of several receiver stations, operate `byrst issuing a ystarting pulse of greater length than all followingpulses of the code combination. The starting pulse places all receiverstations in ready condition. Then a call signal proper, composedof'pulses and spaces of given individual length, is

released in the transmitting station andsimultaneouslyin all receivingstations. At the termination of the selecting operation, an acousticalor optical signal is issued only in the one receiving station whose ownsignal code coincides with that of the particular call received. For yexample, the call signal may comprise three selection criteria formed bythree pulses of given respective lengths. After termination of the lirstcode pulse, all of those receiving stations that are set for avdifferent length of the rst pulse, revert to inactive condition. Thisis re-I l 'peated at the end of the second and third pulses so thatafter termination of the'complete composite call signal, only the onereceiver station remains inready condition' in which all pulse lengthsof its own signal code coincide with those of the calling signal. f

According to the known methods of this type, `thetransi station mustalso be provided with data storing devices which respond tooccurrenceofcoincidence of the pulse length of each individual selectioncriterio-n. It is further a Patented oct. 1o, 1951 selector pulses, andwhich, conjointly with the iirst pulse delaying stage, operate insuch amanner that the next following pulse-delay stages and the signaltransmitter ystage are lsupplied with an input pulse only if the outputpulse .of each precedingdelay stage coincides with a selector pulse.

The invention will be further described andv explained with reference tothe drawing showing, by way of example, an embodiment of a receivingdevice `for response to a calling signal composed of two selectioncriteria, the signal being transmitted by radio, and the deviceoperating on the continuous-current (normally-on) principle.

FIG. l is a schematic block diagram of the receiving station. n

FIG. 2 shows the complete circuit diagram of the receiving station; andf p FIG( 3 is a graph showingpulse diagrams for explainingthe'kfunctioning of the individual stages of the receiver.

` According to the block diagram of FIG. 1,'the receiver comprises yahigh-frequency stage 1 for amplifying the call ysignal received by anantenna 2in form of a pulsemodulated high-frequency signal on a carrierfrequency of 30,000k c.p.s.,'for example. The receiving device furthercomprises two pulse delaying stages 3, 4 and a signal transmitter stage5 connected in cascade through coincidence gating devices 6 and 7. Theincoming selector pulses control the first pulse delaying stage 3 and,through a demodulator 8,'the coincidence gates 6 and 7 in such a mannerthat 'a second pulse delay stage 4 and the signal generating stage 5are` supplied with an input signal only y if the output pulse of each`preceding pulse delay stage coincides with the selector pulse. Thesignal generator stage 5 comprises a tone-frequency oscillator and anelectroacoustic transducer for producing an audible call signal.

In FIG. l; the signal leadsfare shown by full lines, the power feederleads by broken lines, and the control leads by dot-and-dash lines. Thehigh-irequency stage 1 is energized directly from the current source,whereas the other stages are supplied with energizing current through anelectronic switch 9 whichis closed rby the starting pulse of thehigh-frequency call signal rectified ina rectifierf10. Once a startingsignal isreceived, the electronic necessary to providemeans whichdisconnect the receiver by clearing the signal storing devices whentheselection is interrupted. 1 n

It is an object of my invention `toprovide an improved selective callmethod which `affords greatly simplifyingv the receiving stations. byobviating the need for theabovef mentioned accessory devices. f, l

For this purpose, and in accordancewith my invention, the end pulse of aselection criterion is simultaneously used as the starting pulse forthenextfollowing yselection criterion, and the length' ofA the selectionlpulses'is made equal to, or smaller-thamthe step length between twoselective pulse spacings. Eor transmitting the rcall signal, thenormally-on or the normally-.oit principle can be employed, theselectionpulses` in theiirst case `being formed by current pulses andinthe lattercase by current pauses.

According to another feature of the invention, a device for receivingselector calls issued by the above-described method, comprises pulse,delayingstages equal in number to that of the selection jcriteria beingused,y ,the timing intervals of these stages being characteristic of`each particular receiver. The device according to the inventionisfurther provided with a signal transmitter stage, andthe `time-delaystages are interconnectedv in `cascade through switch 9 is kept closedduring the current pauses within each selecting operation..y Duringtheoperating period ofthe signal generator stage 5, a control voltage,maintaining'the electronic -switch 9 closed, is derived fromr thatgenerator stage. Consequently, in the idle 'condition of vthereceiving'device, only the high-frequency stage 1 is energized bycurrent, whereas all other stages are switched on only when receiving acall signal. f

Details of thereceiving device will now be described with reference toFIG. .'2; i f a f The high-frequency stage, comprising a transistor T1,operates in class B operation when the receiving device is idle, butconverts to class A operation after the other stages,` are switched on.4Consequent1y,ythe power requirements of the:` receiver in idle conditionare vir-tually zero.v Usedlas` the .antenna is a `ferrite yrod F whichcarriestheicoil vL1 of a tank circuit L1, (l1 tunedy to the carrierfrequency (for example 30,000 c.p.s.) of the calling signal.V .Thechosen quality factor of the tank circuit is relatively low..(Q=1 2)`for'keeping the transmission of the high-frequency pulses -asundistorted asA possible. "Two resistors R1 and R2 serve `forstabilizingthe emitter-to-base current of transistor T1. The amplifiedhigh-frequency signal is taken from the collector .f of transistorTl'andis supplied through a capacitor C8 respective coincidencegates:whichare,controlledhythe 1.

and a diode D2 to the first pulse delaying stage. This stageand thesecond pulse delay stage, are formed byrespectivev monostablemultivibrators of the same design, comprising transistors T3, T4 and T5,T6. In idle condition, the..transistorsv T4. and y--Tt arein conductivecondition. The resistance capacitance members R9, C11 and R16, C14,determine the time constant of the respective pulse-delaying operations,the pair of capacitance values for capacitors 4C11 and C14 beingdifferent in each receiver from those of the other receivers of a group.The emitters of transistors T3 to 'T6 are all grounded through thecommon emitter `resistor R1. As a result., a positive 'bias voltage isapplied ,through resistors R7 and R14 to the bases of respectivetransistors T3 and T5 to prevent self-starting of the multivibrators.

Fundamentally, the time constant of the pulse delay depends upon theleakage current of the transistor T4 or T6, this current bei-ngdependent .upon temperature. For temperature compensation, `a voltage isintroduced through the resistor R9, R16 which follows the same law oftemperature-responsive .change as the leakage current. This renders t-hetime constant independent of temperature. The compensating voltage istapped from a potentiometer resistor R21 connected in the collectorcircuit of a transistor T'7 .of .the same type .-as the transistors T4and T6.

The signal generator stage .also consists vof a monostable multivibratorwith transistors T8 and T9 in which, however, the ampliiier stage (T9),.conducting no current in the idle condition, .is designed as anVaudioffrequency oscillator .feedback connected .in itself. The kcontrolvoltage for .the other ampliiier (T8) is obtained by rectifying theaudio-frequency voltage. The 4load vimpedance of theoscillator-.transistor T9 is formed by la tank .circuit composed of aninductance coil 15a-nd a capacitor C22. Another Acapacitor C21 is.connected -parallel to capacitor C22 through .a diode D10. A resistor.R24 serves `for discharging the capacitor C21, and adiode D9 isinserted for tie-coupling .the capacitor 4C21 from 'the base .oftransistor T8 relative to positive pulses. Inductively linked with coilLS is a |feedback-.coil .-L6. The feed-back transformer L5, L6constitutes .the V.excitation system .of an electroacoustic transducerfor producing an audible signal whose frequency may Vbe's300() ,c,p.sfor example. To prevent the audio-frequency oscillator lfrom building uposcillations Vdue `to the transistor leakage current, the base of.transistor T91is supplied with positive bias voltage through a resistorR26. The bias voltage is obtained :from the high-frequency signal b yrectification. Used as rectier .for this purpose .is a voltage-@doublingconnection formed by diodes D3., D4 andeapacitors C7, C20.

The output of each pulse delay stage is `connected with .the nextfollowing stage :by la Icoincidence gating device. Y The coincidencegates y:consist of the series connection vof a capacitor C12 or C15 witha diode DS .or D6 `biased in the lblocking fdirection. The bias ofdiodes D and D6 is so chosen that the youtput pulse of eachmultivibrator is transmitted rto the input of the next following stageonly :if a selector ,pulse simultaneously controls the appertainingcoincidence gate in the biasreducing sense. Since vthe transmission ofthe Vselector pulses is elected fon the continuous-current (normallyon)Aprinciple so ,that the selector :signals lare formed by the currentpauses, .the bias voltage is .derived from the highefrequency signal andhence Yvanishes when a Yselecting -signal (pause) is being received. Thehigh-frequency signal is rectified by ra rectiier GR Vwhich istransformercoupled with `the hig`h-frequency sta-ge, l.the couplingbeing effected by a coil L3 which, together with a capacitor'C, forms atanlk `circuit tuned Nto the high frequency. The bias voltage is taken'off at a circuit point between 1resistors R11 and R12 ion the one hand,and at a circuit pointl between resistors R18 and .R19 .on the otherhand.

The resistors R11 :and :R18 serve to discharge the capacitors C12 "andC15. The resistors R12 and :R19 serve to ,mutually zdecouple thecoincidence igates.

The :receiving device is supplied with current from .a single .battery(ttor example .2:6v.l).. With the exception of the :high lfrequencystage directly connected to `the feed buses, all .stages :of fthe.device are .energized through an electronic switch comprising atransistor T2 in grounded-collector connection. The normallyopenelectronic switch is closed =at thebeginning of la cal-ling signal whichmakes the transistor T2 conducting. The baseemitter voltage forcontrolling the transistor T2 is obtained by recti-fying thehigh-frequency signal ata diode D1 which is likewise transformer-coupledwith the high- Ifrequency stage. A capacitor C4 serves ttor smoothingthe rectified voltage and 'also as a storer for maintaining theelectronic switch in closed condition during the current pauses of thesignal. A .resistor R4 reduces the leakage current of transistor T2. Therelectronic switch is kept in closed condition beyond the duration ofthe selecting operation during the active period of the signal generatorstage, this being effected by a control voltage derivedlfrorn the signalgenerator stage. This control voltage is obtained by rectifying theaudio-frequency voltage taken trom the emitter of transistor T8 by meansof the voltage-doubling connection composed of the diodes D7, D8 and thecapacitors C16, C4.

An example .of types and parameter values of the circuit componentsshown in FIG. 2 and used in 'a tested embodiment of the device arelisted in the following table, it being understood that these data maybe` changed in accordance with the particular requirements or desiderataof .any particular application.

^ T2, T9 0G76. T T8 OC710. D1 D10 DASS. GR 4xDN 34a. L1 .324 turns, 7mh. L2 250 turns. L3 77 turns. L4 420 turns. L5 360 turns. L6 120 turns.R1A 220 ohm. R2 330011111. R3 270 ohm. R4 3.3K ohm. R5 100K ohm. R6,R113 2.2K ohm. R7, R14 10K ohm. R8, R15 10K ohm. R9, `=R16 27K ohm.R110, R17 2.2K ohm. R11, R118 22K ohm. R12, 1R19 A6.8K ohm. R20 6.8Kohm. R21 150 ohm. R22 1K ohm. R23 15K ohm. 'R24 15K ohm. R25 12K ohm.

6 100 ohm.

1 C2 =10 ,wf C3 2 nf C4 2 ,if C5 10 pf C6 0.5 of C7 2 nf. C8 2 nf. C93:nf. C10, C13 5 nf. C12 1.5 nf. C15 2.1 nf. C16 `0.1 af. C17 50 n'f.C18 8./Lf. O19 3311i. C20 10 nf. C21 0.25 tlf.

C22 0.5 pf.

il. u1 The performance of the above-described receiving device will beexplained with reference to the pulse diagrams (a) to (e)'in FIG. 3.FIG. 3a illustrates the pulse sequence of a complete call signal used int-he callsignal transmitter for modulating the `carrier frequency. Thecall signal commences with the starting pulse AI when the continuouscurrent is switched on.y The starting pulse is followed by thelirstselector pulse 1.WIv consisting of a current gap (pause) o-f theduration 1- (for example 0.3 millisecond). The second and third selectorpulses 2.Wl and 3.WI respectively, follow the rst pulse after givenintervals whose durations constitute respective selection criteria. Thesecond selector pulsey 2.WI is simultaneously the end portionof theiirs't selecting criterion and vt-he starting portion of the secondvselecting criterion.

` During this interval, the audio-frequency oscillator is in In thepresent example, "the secondk and the third selecting pulses may occupyany one of six. different positions relative to the preceding selectingpulse, these six possibilities being indicated kby vert-icaldot-and-dash lines (pulse centers) numbered from 1 to r6.' Accordingly,six selective pulse spacings are available for each selecting criterionso that, by combination, 36- dilerent call signals can be madeavailable. The steplength between two selector-pulse spacings is equalto the ylength of the selecting pulse. The endof the pulse sequence isformed by a terminating pulse SI. rllhe starting pulse AI, rectifiedinthe receiving device by the diode D1, charges the capacitor C4. As aresult, the base potential of transistor T2 is reduced, thus turning thetransistor TZ on. 'Ihis closes the 'feed-current circuit for thereceiver stages that are not energized in the feeder line SpL (FIG. 2)is in accordance'with the diagram shown in FIG. 3b.

Assume that the time constants of the two pulse delay stages are adaptedto make the receiving device, namely its siganl generator stage, respondto the particular call oscillation and produces the acoustic signal(FIG. 3e).

When the continuous current ultimately vanishes a short time (2r) aftertermination of the third selecting pulse 3;,WI, thev calling signal isterminated. Atthis moment the electronic switch TZ of the receivingdevice in all receiver stations, with'the exception of the one selected,is'opened. In the selected receiver station, the control voltage derivedfrom the now yoscillating audio-frequency generator keeps the electronicswitch in closed condition until the multi-vibrator ofthe signalgenerator stage reverts to the starting condition. The repeated responseof the iirst pulse delay stage a-t the end of the third selecting pulse(FIG. 3c) has no disturbing effect upon the abovedescribed operation.

The invention permlts' of numerous changes and modications, incomparison with the above-described embodiment of the receiving devicebuilt and tested, with respect lto the design ofthe individual stagesandthe number-of stages employed. For example, the invention may beapplied for more than two selecting criteria and for more' y than six(for example 10) selectable impulse spacings of the idle condition ofthe receiving device. ,The voltage at v signal according to the pulsediagram of FIG. 3a, in

which the largest selectable pulse spacing is chosen for the twoselecting criteria. At the end of the first selecting pulse LWL thefirst multi-vibrator (T3, T4) is triggered due to the fact that thetransistor T3 is turned on by the pulse peak which is active on thecollector 4and is derived from the ascending flank of the first fullpositive highfrequency wave of the continuous current now again flowing.After elapse of the given interval of time 6r, the multi-vibratorreverts back to the stable starting condition (FIG. 3c). This causes apositive pulse peak to occur at capacitor C12 and trigger the secondmulti-vibrator (T5, T6). However, the just-mentioned pulse peak,appearingas the output signal of the first pulse delay stage, istransmitted to the input of the second pulse delay stage only if thisoutput signal occurs within an interval of time during which a secondselecting pulse 2.WI is effective. The continuous current flowingbetween two selecting pulses produces at diode D5 a bias voltage in theblocking direction which is chosen so large that the amplitude oftheoutput signal is not sufficient to control the diode DS for conductancein the 'forward direction. During the active duration of the secondselecting pulse 2.WI, the continuous current is interrupted and theabove-mentioned bias voltage vanishes so that the output signal of thelirst delay stage occurring within this time interval can release thenext following pulse delay stage. Similar conditions obtain relative tothe transfer of the output pulse (FIG. 3d) from the second pulse delaystage to the signal generator stage. That is, the signal generator stageresponds only if, like in the preceding example, thek pulse peakproduced when the second multi-vibrator (FIG. r3) reverts to stableinactive condition, coincides in time with the third selecting pulse. f

The multi-vibrator (T8, T9) of the signal generator stage, afterresponding, remains in its active condition,

adselecting criterion, thus permitting an increase in the,

number of receiving stations that can be reached by call signals from asingle transmitter. Each additional selecting criterion merely requiresthe 4addition of another pulse delay stage and another coincidence gate.The permissible enlargement in this sense is limited only by theattainable tolerance of the pulse lengths and pulse spacings. Thislimitation, however, vanishes if the step lengths of the selective pulsespacings are not equal among themselves as in the above-describedexample, but are in accordance with av geometric series. f

Particular advantages of the receiving device according to the inventionare its extremely small space requirements and slight currentconsumption. Thev above-described tested device, for example, occupiesno more space than a cigarette package (l0-pack). The invention,therefore, is particularly suitable 'for personnel locating sys-temswith portable or pocket receivers. Experience has also shown thatthereceiving device according to the invention is virtually insensitiveto spurious signals. f

The duration of each call can be prolonged by periodically rrepeatingthe call signal. This causes the abovedescribed functioning sequence inthe receiving device tok repeat itself. By suitable choice of therepetition frequency (for example l0 c.p.s.) the audibility oftheacoustic signal over noises, in comparison with a continuous tone, canbe greatly improved without increase in tone intensity.

I claim:

1. A receiving device selectively callable by a coded call signalcomposed of a starting pulse, followed by a given number of successivecode pulses, with the time spacing between each pulse and the next pulsebeing determined according to the code of the called receiving deviceand constituting the selection criteria, which comprises a signalreceiving stage, pulse delay stages equal in number to that of theselection criteria of the call signal, said delay stages havingrespective timing periods which, in totality, are distinctive of theparticular call signal to which the receiving devicev will respond, alocal-signal generating stage for producing a local signal under controlby a call signal received, a first one of said pulse delay stages beingconnected to said signal receiving stage for response to the startingpulse, coincidence gates, said pulse delay stages being connected incascade with each other through respective ones of said coincidencegates, the last pulse delay stage being connected to said signalgenerator stage through another one ofsaid coincidence gates, whereby acall signal being received by said receiving stage controls the firstpulse delay stage, and means connecting the output of the signalreceiving stage to said coincidence gates for passing the output pulsefrom one pulse delay stage through a coincidence gate to each' nextpulse delay stage and 'to said signal generating stage only when theoutput pulse of each preceding pulse delay stage coincides with one ofsaid selection criteria.

2. In a selectively callable receiving device, according Vto claim 1,all of said stages having respective electronic members, feeder currentsupply means connected with said receiving stage for energizing itduring receptive condition of the device, a normally open electronicswitch connected between -said cur-rent supply means and all of saidother stages, said electronic switch having a switch control circuitconnected with s-aid receiving stage for closing said yswitch inresponse Io reception of said stat-ting pulse, means connected with:said switch control circuit for keeping said switch closed during.current pauses of the calling signal, and voltage supply meansconnecting said signal generator stage with said switch control circuitfor keeping said switch closed during the operating period of saidsignal generator stage.

3. In a selectively callable receiving device :according to claim l,each of said pulse dela-ystages comprising a monostable multivibrator,each of said coincidence gates comprising a capacitor and a diodeconnected in series wi-th each other between the output of one of saidmultivibrators land the input of the lnext following one of said stages,`and .bias voltagemeans connected with each of said ldiodes for applyingthereto a bias voltage in :the block-y ing Sense which 'is reduced to avalue required for passing the output pulse of said one multivibrator tosaid next following stage `only when a code pulse is appliedsimultaneously with said output pulse to said coincidence 4gate in thediodeebias reducing sense.

4. IIn a selectively -callable receiving device according to claim l,said signal generator stage consisting ,of a monos-table multivibratorhaving two amplifier stages of which one is normally de-energizcd, saidone amplifying stage consisting of an internally feedback-connectedaudio-frequency oscillator.

5. A selectively callable receiving device according rto claim 4,comprising rectifier means connected to said audio-frequency oscillator,and said other amplifying stage having a control circuit connected tosaid rectifier means for deriving control voltage from said oscillator.

6. In a selectively callable receiving device according to claim 5, saidone amplifying stage having a load impedance consisting of anoscillatory tank circuit, a capacitor, and a rectifier connecting saidIcapacitor with ,s aid tank circuit in parallel relation thereto.

References Cited in the tile of this patent UNITED STATES PATENTS

